The phrase

*a number*means an arbitrary variable, let's call it x:

x

The square root of a number means we raise x to the 1/2 power:

sqrt(x)

the square root of a number increased by 5 means we add 5 to sqrt(x):

sqrt(x) + 5

twice the square root of a number increased by 5 means we multiply sqrt(x) + 5 by 2:

2(sqrt(x) + 5)

The phrase

*is 23*means we set 2(sqrt(x) + 5) equal to 23:

**2(sqrt(x) + 5) = 23**